add blue gradient background

in_one_weekend/src/vec3.zig

@@ -0,0 +1,78 @@
+const math = @import("std").math;
+
+pub const Vec3 = packed struct {
+    x: f32 = 0.0,
+    y: f32 = 0.0,
+    z: f32 = 0.0,
+
+    pub fn add(u: Vec3, v: Vec3) Vec3 {
+        return Vec3{
+            .x = u.x + v.x,
+            .y = u.y + v.y,
+            .z = u.z + v.z,
+        };
+    }
+
+    pub fn sub(u: Vec3, v: Vec3) Vec3 {
+        return Vec3{
+            .x = u.x - v.x,
+            .y = u.y - v.y,
+            .z = u.z - v.z,
+        };
+    }
+
+    pub fn mul(self: Vec3, scalar: f32) Vec3 {
+        return Vec3{
+            .x = self.x * scalar,
+            .y = self.y * scalar,
+            .z = self.z * scalar,
+        };
+    }
+
+    pub fn div(self: Vec3, scalar: f32) Vec3 {
+        return Vec3{
+            .x = self.x / scalar,
+            .y = self.y / scalar,
+            .z = self.z / scalar,
+        };
+    }
+
+    pub fn length(self: Vec3) f32 {
+        return math.sqrt(self.x * self.x + self.y * self.y + self.z * self.z);
+    }
+
+    pub fn dot(u: Vec3, v: Vec3) f32 {
+        return u.x * v.x + u.y * v.y + u.z * v.z;
+    }
+
+    pub fn cross(u: Vec3, v: Vec3) Vec3 {
+        return Vec3{
+            .x = u.y * v.z - u.z * v.y,
+            .y = u.z * v.x - u.x * v.z,
+            .z = u.x * v.y - u.y * v.x,
+        };
+    }
+
+    // pub fn unit_vector() Vec3 {
+    //     return
+    // }
+};
+
+pub fn unitVector(vec: Vec3) Vec3 {
+    return vec.div(vec.length());
+}
+
+pub const Point3 = Vec3;
+pub const Color = Vec3;
+
+const assert = @import("std").debug.assert;
+
+fn assert_cmp(actual: f32, expected: f32) void {
+    const epsilon: f32 = 1e-5;
+    assert(math.fabs(actual - expected) < epsilon);
+}
+
+test "Vec3.length" {
+    const v = Vec3{ .x = 1.0, .y = 1.0, .z = 1.0 };
+    assert_cmp(v.length(), 1.7320508);
+}